Вісник Київського національного університету імені Тараса Шевченка. Серія: фізико-математичні науки
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Fatique durability of smooth cylindrical rods under uniaxial symmetric stretch – compression
Get PDFThe paper proposes a model of fatigue, that is based on the reduction of the carrier mass of the substance at half-cycle compression and its density increase by half-cycle stretching. High tension and volume deformation are linearly related by Hooke\u27s law. Mass and density changes and stress changes depending on the elastic properties of the rod, its initial mass, density and volume are received analytically for each cycle. The model usage limit is a cycle in which amplitude values stress reaches the elastic limit. The proposed model algorithm is implemented in software environment with which the destruction is determined fatigue limit and fatigue. The resulting design value curve is different from the curve of fatigue of gray iron that was investigated. This is due to the fact that scattering of the applied energy on internal friction and heating is not included in the model.Key words: symmetric tension-compression, fatigue model, fatigue limit, fatigue failure energy criterion.Pages of the article in the issue: 82-85Language of the article: Ukrainia
To the modelling of the fatigue cracks propagation in a thin isotropic plates under biaxial asymmetric tension-compression
Get PDFThe modelling of the fatigue fracture process of the thin isotropic infinite plates with cracks under external biaxial asymmetric cyclic loading is considered. The solution of the problem is based on the joint consideration of the fracture mechanics and continuous damage mechanics concepts and using two types of equivalent stress criteria’s. The first one reduces an asymmetrical cyclic load to the equivalent symmetric cyclic load in time of the rupture. The second one reduces a plane stress state in the vicinity of the top crack to a single-axial one. The obtained system of equations of the model a relatively equivalent stress intensity factor allows us to determine the duration of the incubation stage and the rate of fatigue crack propagation in plates with different stress concentrators. The calculated dependences of the crack length, which extends from the circular hole, from the number of load cycles in the infinite aluminum plate with a circular hole at the variation of the parameters of the asymmetrical cycle and the coefficient of the biaxiality loading are constructed.Key words: fatigue crack, biaxial asymmetric cyclic loading, damage.Pages of the article in the issue: 154-157Language of the article: Ukrainia
Steady-state resonant sloshing in upright cylindrical tank due to elliptical forcing
Get PDFThe nonlinear Narimanov-Moiseev multimodal equations are used to study the swirling-type resonant sloshing in a circular base container occurring due to an orbital (rotary) tank motion in the horizontal plane with the forcing frequency close to the lowest natural sloshing frequency. These equations are equipped with linear damping terms associated with the logarithmic decrements of the natural sloshing modes. The surface tension is neglected. An asymptotic steady-state solution is constructed and the response amplitude curves are analyzed to prove their hard-spring type behavior for the finite liquid depth (the mean liquid depth-to-the-radius ratio h>1). For the orbital forcing only swirling occurs. This behavior type is supported by the existing experimental data. Phase lags, which are piecewise functions along the continuous amplitude response curves in the undamped case, become of the non-constant character when the damping matters. The wave elevations at the vertical wall are satisfactory predicted except for a frequency range where the model test observations reported wave breaking and/or mean rotational flows.Key words: sloshing, damping, steady-state waves, orbital forcing.Pages of the article in the issue: 166-169Language of the article: Ukrainia
Plane stress state of a strip weakened by a crack
Get PDFThe plane stress elastic infinite strip problem of a finite longitudinal crack is investigated. The method that can be applied to calculate the stress state and the displacements for an infinite and semi-infinite strip with the longitudinal crack and arbitrary configuration of the boundary conditions is proposed. The main advantage of this method lies in the absence of necessity for use of the apparatus of the matrix differential calculus. Initial problem is reduced to the one-dimensional boundary value problem with the help of the generalized scheme of the integral transform method. By using the inverse integral Fourier transform, the one-dimensional problem is reduced to solving of the system of singular integral equations on a finite interval. The solution of this system was constructed with the help of the method of orthogonal polynomials by means of the second kind Chebyshev polynomials series expansion of the unknown functions. A graph of dependence of the stress intensity factor (SIF) on the geometric parameters of the problem is plotted. It is shown that the SIF for the case of the said strip tends to the SIF for the case of an infinite plane as the width of the strip approaches infinity.Key words: plane elastic problem, infinite strip, longitudinal crack, stress state, stress intensity factor.Pages of the article in the issue: 182-185Language of the article: Ukrainia
The mixed unsteady heat conduction problem for a half-infinite hollow cylinder
Get PDFAnalysis of temperature fields is important for many engineering applications. The account of actual operating conditions of these structures frequently leads to mixed heating condition. The authors of this paper developed a new effective method of solutions derivation for mixed boundary-value unsteady heat conduction problems. This paper considers the cylinder with at the part of surface of which the temperature distribution is known. Outside this area the heat transfer by Newton\u27s law is performed.To the heat conductivity problem it is applied the Laguerre integral transformation in time variables and integral Fourier transformation in spatial variable. As a result the triangular sequence of ordinary differential equations is obtained. The general solution of these sequences is obtained in the form of algebraic convolution. Taking into account the mixed boundary conditions leads to dual integral equations. For solution of this problem it is proposed the method of Neumann\u27s series. By this method the problem is reduced to the infinite system of algebraic equations, for which the convergence of reduction procedure is proved. Finally, the unknown temperature is submitted as a series of Laguerre polynomials. The coefficient of these series is Fourier integrals.Key words: unsteady heat conduction problem; mixed boundary conditions; Laguerre polynomials; dual integral equations.Pages of the article in the issue: 222-225Language of the article: Ukrainia
Cutting-out method in the problem of longitudinal shear of anisotropic half-space with a crack
Get PDFThe previously developed direct cutting-out method in application to isotropic materials, in particular to bodies with thin inhomogeneities in the form of cracks and thin deformable inclusions is extended to the case of taking into account the possible anisotropy of the material. The basis of the method is to modulate the original problem of determining the stress state of a limited body with thin inclusions by means of a technically simpler to solve problem of elastic equilibrium of an infinite space with a slightly increased number of thin inhomogeneities, which in turn form the boundaries of the investigated body. By loaded cracks we model the boundary conditions of the first kind, and by absolutely rigid inclusions embedded into a matrix with a certain tension – the boundary conditions of the second kind. Using the method of the jump functions and the interaction conditions of a matrix with inclusion, the problem is reduced to a system of singular integral equations, the solution of which is carried out using the method of collocations. Approbation of the developed approach is carried out on the problem of elastic equilibrium of anisotropic (orthotropic in direction of shear) half-space with a symmetrically loaded very flexible inclusion (a crack) at jammed half-space boundary. The influence of inhomogeneity orientation and the half-space material on the generalized stress intensity factors were studied.Key words: antiplane shear, anisotropy, cracks, thin elastic inclusions, cutting-out method.Pages of the article in the issue: 24-27Language of the article: Ukrainia
Architecture of the Platform for the E-Government Open Data
Get PDFE-Government is a set of pervasive technologies and automated processes now. The open data plays a crucial role in the successful implementation of this concept. The Open Data Platform (ODP) architecture is described here as the framework for the open data access systems implementation, including specific requirements. The proposed architecture and its components were discussed in this paper in detail for its availability, productivity, and reliability. The open data subsystem based on the architecture presented here was developed for the Jordan Government and was successfully implemented and tested. Thus, this architecture showed its viability.The focus of the paper is the detailed analysis of the proposed ODP architecture and its characteristics. The ODP is a significant system for the mature e-Government. We propose here the architecture for it with usage-proven characteristics. This fact adds the value to the e-Government framework stability, and significant characteristics and improves the overall quality of the system.Key words: e-government, open data, digital transformation, digitalization, system architecture, high availability, high performance, open data platform.Pages of the article in the issue: 70 - 76Language of the article: Ukrainia
Processes of formation of positive ions at the electron - thymine molecule interactions
No full textThe work is aimed to solve the key problems of modern biophysics related to the study of fundamental mechanisms of interaction of ionizing radiation on living cells and stability of biological systems to its influence. The obtained data and their generalizations create a basis for understanding the interaction mechanisms and stability of biological systems to its influence. Investigation is aimed on the obtaining the new priority data about the characteristics of the life important biological molecules, establishing the mechanisms and features of dissociative capture, excitation and ionization under the slow electrons; the study of the influence of intermolecular interactions on these processes and solution of some applications concerning the definition of physical stability of biomolecules in different states of aggregation. The AM1 method that was used in research is a semi-empirical method for the quantum calculation of molecular electronic structure in computational chemistry. It is based on the neglect of differential diatomic overlap integral approximation and investigates the processes of formation of positive ions, which are formed during the interaction of thymine molecules with slow electrons. Fragmentation model of thymine molecules under electron ipmpact is proposed. Six most likely bond breaks in the cyclic structure of thymine molecular ion are identified. The obtained results are in good agreement with experimental data.Key words: thymin, positive ion, electron, fragmentation.Pages of the article in the issue: 104 - 107Language of the article: Ukrainia
Analysis of reservoir’s mass influence on the system free – surfaced liquid and spherical reservoir
Get PDFWithin the framework of combined motion the effect of ratio of masses of reservoir and liquid on the behavior of a free surface of liquid in the reservoir of spherical shape is studied. We suppose that liquid is ideal and it fills partially the reservoir. Mathematical modelling is done on the basis of the model, which takes into account combined character of nonlinear dynamics of liquid and the reservoir. Examples were done based on mathematical model of combined motion of liquid in spherical reservoir and free-surfaced liquid under harmonic force disturbance in horizontal direction. Two cases of the ratio of masses in the system are considered. First, the mass of the reservoir is 5 times less than the mass of the liquid; the mass of the reservoir is 5 times greater than the mass of the liquid. In order to identify specific features of the system behavior, the results were compared with the results for liquid behavior in cylindrical and conical reservoirs. It was ascertained that mass increasing has no tendency of converging to a steady mode of motion, which was confirmed experimentally. Distinctions of manifestation of nonlinear processes for the below-resonance, near-resonance and above-resonance modes are shown. We note manifestation of nonlinear effects such as modulation, the presence of high-frequency normal modes of oscillations, antiresonance and drift of the mean of oscillations.Key words: reservoir, free-surfaced liquid, drift of oscillation, modulation.Pages of the article in the issue: 110-113Language of the article: Ukrainia
Realization of calculation of bended deformations of teeth of gear wheels from composites
Get PDFIn this work the implementation of calculation of bended deformations of teeth of gear wheels from composites is considered. To solve the problems considered (calculation of stress-strain state), an automated technique was developed and a program module was created. The flexural deformation of a toothed tooth tooth from a fibrous material with anisotropic properties under the action of concentrated force in various distinctive points on the surface of the tooth is researched. To calculate the deformation of gear wheels from metals and plastics, a program is also developed in the Delphi environment, which makes it possible to implement the calculation of the coefficient of bending deformation of the tooth of the toothed wheel. Three models of the tooth were considered: in the form of a wedge, parabolas and evolvents with a gallet. The algorithm is developed and the program, which implements the calculation of the bending coefficient coefficient for three models of the gear tooth of composites, is developed.Key words: deformation, composite, evolvent, gear wheel, software complex.Pages of the article in the issue: 134-137Language of the article: Ukrainia